Pronouns improperly serialized as null when should be empty string

Describe the bug
When using the endpoint GET /users/{id}/profile, the pronouns field in user_profile is sent as null on Spacebar, but as an empty string ("") on Discord (if the user has no pronouns set)

To Reproduce
Send a request to GET /users/{id}/profile on Discord.
See the response data:

{
...
"user_profile": {
    "bio": "Level 6 warlock charisma caster, professional gnome adventurer, you can find at your local tavern killing rats in the basement",
    "accent_color": 16777215,
    "pronouns": ""
},
...
}

Send a request to GET /users/{id}/profile on Spacebar.
See the response data:

{
...
"user_profile": {
    "bio": "",
    "accent_color": null,
    "banner": null,
    "pronouns": null,
    "theme_colors": null
},
...
}

Expected behavior
Instead of serializing as "pronouns": null, it should probably be "pronouns": "", to mirror Discord

Env and Software info
Tested on the staging server, old.server.spacebar.chat

Start at GET /users/{id}/profile and trace how user_profile.pronouns is serialized, comparing the current Spacebar response with the Discord example. Done when users without pronouns receive an empty string instead of null, with coverage for this response behavior if the endpoint has existing tests.